In the Free Company Data Product, the field Accounts.AccountCategory is meant to show the type of the filed accounts of a company. It seems, that for certain account types (e.g. 'Micro company accounts') the field is just empty in the bulk file.Example: https://beta.companieshouse.gov.uk/company/07354115/filing-history show 'Micro'. In the bulk file, the entry is empty for this company.